Stromal tumors of the gastrointestinal tract represent relatively rare lesions that are thought to arise from connective tissue elements located along the entire length of the gut. For many years these tumors have been the subject of much controversy and debate in the literature regarding their histogenesis, criteria for diagnosis, prognostic features, and nomenclature. Only a minority of these lesions, mainly those confined to the esophagus and rectum, have been shown to correspond to mature, well-differentiated types of neoplasms such as leiomyoma or leiomyosarcoma of the conventional type. The majority of stromal tumors of the gastrointestinal tract correspond to a heterogeneous group of lesions that have as their common denominator an immature proliferation of epithelioid or spindle cells arising from its muscle layer and showing partial or incomplete myoid, neural, ganglionic, or mixed features of differentiation. This review will attempt to summarize our current knowledge and understanding of these lesions based on review of the literature and the author's personal experience, with an analysis of the criteria for distinguishing between benign and malignant tumors, and a proposal for a working classification for these lesions.